The use of oxygenates, i.e., a compound containing oxygen, as gasoline additives to reduce carbon monoxide and soot can increase air pollution, in particular ground-level ozone and smog. In addition, the use of ethanol alone or in gasoline blends can create problems for fuel equipment not designed to handle the more non-polar hydrocarbonaceous petroleum fractions commonly known as gasolines. The polarity and corrosivity of ethanol or ethanol-containing fuels can create new problems for the fuel industry.
These ethanol or ethanol-containing fuels can create engine wear from reduced naturally occurring lubricating species in the fuel and increased corrosion or increased deposit formation. Corrosion and deposit formation can reduce drivability or fuel economy, or even cause complete failure. Corrosion inhibitors are frequently deployed to mitigate these negative effects. Further, the use of fuel oxygenates has increased the need for effective corrosion inhibitors.
In general, corrosion inhibitors protect a metal surface through the formation of a passivation film on the metal surface. This passivation layer oil wets the metal surface, which in turn prevents contact of the metal from the corrosive nature of the fluids. Typically, corrosion inhibitor formulations of this type contain a variety of aliphatic organic surfactant molecules ranging from, but not limited to, amines, quaternary amines, imidazolines, phosphate esters, amides, carboxylic acids, or combinations thereof.
Often, organic thiol compounds are added in low concentrations to these corrosion inhibitor components to increase the effectiveness of the traditional corrosion inhibitor molecules. It is believed that these organic thiol molecules create a stronger passivation layer on the metal surface which also increases the persistence of the protective film. In most examples, the sulfur based component consists of a primary thio/mercaptan (e.g., 2-mercaptoethanol or mercaptoacetic acid). In some instances, however, such thiol based formulations can degrade at elevated temperatures (e.g., during storage at elevated temperatures) to release volatile sulfur-containing vapor/gases (e.g., mercaptans, sulfur dioxide, hydrogen sulfide, and/or carbonyl sulfide).
Recently, government guidelines were released requiring gasoline being sold within the United States to contain less than 10 ppm sulfur on an average annual basis starting on Jan. 1, 2017. As a result, additives, e.g., corrosion inhibitors, must also have a low sulfur content or have a waiver from the EPA to allow them to be added, if the addition of the additive causes the finished gasoline to exceed the 10 ppm sulfur annual average.
Thus, there is a need to develop effective corrosion inhibitors that contain a low sulfur content.